Field of the Invention
Exemplary embodiments of the present disclosure relate to a bucket assembly for replacing an old bucket provided with a turbine and a method for replacing the same, and more particularly, to a bucket assembly for replacing an old bucket provided with a turbine and a method for replacing the same capable of easily replacing only a damaged bucket without sequentially disassembling the already installed buckets though a notch opening upon replacing the damaged bucket among the already installed buckets in a tangential entry type dovetail.
Description of the Related Art
Generally, a steam turbine is an apparatus for rotating buckets with blades with high temperature and high pressure steam generated from a large-capacity boiler for a power station to convert heat energy into rotary power which is kinetic energy and is generally divided into a high pressure turbine, an intermediate pressure turbine, and a low pressure turbine to maximize efficiency.
Generally, the steam turbine includes a casing forming an appearance and a frame of the turbine and a rotor rotatably installed in the casing.
Generally, each bucket includes blade parts and dovetails formed at ends of an inside in a radial direction of the blade parts.
Generally, the dovetail may be largely divided into a tangential entry type, an axial entry type, a pinned finger type, and a key axial shape depending on a method for coupling the above-mentioned dovetail with the rotor.
FIG. 1 is a perspective view of a state in which a bucket is coupled with a male dovetail in the existing tangential entry type dovetail.
As illustrated in FIG. 1, a rotor 10 or an outer circumferential surface of a rotor wheel 20 is provided with the male dovetail 30. A portion of the male dovetail 30 is provided with a notch opening 40, such that a plurality of buckets 50 are sequentially inserted in a tangential direction of the rotor through the notch opening 40. Although not illustrated, the final bucket inserted into the notch opening 40 may be additionally coupled with a separate fixing member not to be separated through a gap of the notch opening 40.
Generally, the bucket is eroded by foreign matters or hygroscopic moisture introduced into the casing of the turbine during the operation of the steam turbine. As such, the damaged bucket reduces the efficiency of the turbine and therefore needs to be necessarily replaced.
However, to replace the damaged bucket in the existing tangential entry type dovetail, the already installed bucket as well as the damaged bucket needs to be sequentially disassembled through the notch opening. Even when the damaged bucket is installed near the notch opening 40, the plurality of normal buckets need to be disassembled through the notch opening 40, which causes inconvenience. In addition, to replace the bucket installed at the exact opposite side of the notch opening 40, the bucket corresponding to a half of the total number of buckets coupled with the male dovetail needs to be disassembled through the notch opening 40 and therefore the replacement of the damaged bucket is very uncomfortable.
Further, to replace the damaged bucket in the existing tangential entry type dovetail, the damaged bucket needs to be disassembled through the notch opening, and therefore the replacement time and the replacement costs of the damaged bucket may be increased.
In addition, to replace the damaged bucket in the existing tangential entry type dovetail, the bucket needs to be disassembled through the notch opening in a reverse order to the assembled order. As a result, the rotor or the rotor wheel provided with the male dovetail may be secondarily damaged.
Further, to replace the damaged bucket in the existing tangential entry type dovetail, shroud latching occurs during the process of disassembling the buckets through the notch opening and thus Shroud align is misaligned, thereby reducing the efficiency of the turbine.